@spud
yeah these things take forever to fully burn in, I'm at almost 500 hours on mine and I would say they still have a little ways to go.
That being said do not expect for the brightness to disapear with burn in. They certainly do balance out quite a bit, and the sibilance disapears aswell. But even with burn in I wouldn't call them neutral, they are certainly still bright. The bass will come out a little bit, to the point where it is always distinguishable, yet it will never be anything more than analytical. When I first got my k701's the bass would often become lost because it was so overpowered, this is no longer the case. The soundstage also improves ever so slightly
I can't tell you whether or not you will enjoy the k701 after burn in, but I can say that these headphones are not for everybody. Perhaps if you want anything but a bright sounding headphone then you should look into returning them. For me though they are simply fantastic because of what they can do with acoustic tracks.